An overview of theoretical and experimental results on first- overtone (FO) CO laser is presented. A special attention is paid to the quite new results jointly obtained at the Lebedev Physics Institute (Russia), TRINITI (Russia) and Air Force Research Lab (USA). Efficient multiwavelength pulsed FO CO lasing with output efficiency up to 11% and specific output energy up to 50 J/l Amagat is observed within the spectral range of 2.5 - 4.1 micrometer corresponding to the vibrational transitions V + 2 yields V from 6 yields 4 up to 37 yields 35. Single-line frequency tunable FO CO lasing on the wavelengths from approximately 2.7 up to 4.2 micrometer with the maximum output efficiency up to approximately 1% is also observed. Multiline and single-line lasing on 430 ro- vibrational lines is obtained. Theoretical calculations based on the experimental data predict that multiline FO CO laser efficiency can be enhanced up to 20%. FO CO laser with output efficiency and specific output energy comparable with those of CO2 laser and spectral region of lasing covering that of HF and DF lasers can be considered as a potential source of high-power IR radiation for frequency selective laser ablation.